Moving handrails have been developed for escalators, moving walkways and other similar transportation apparatus. The basic profile for such handrails has now become fairly standardized, even though the exact dimensions may vary from manufacturer to manufacturer. Similarly, all conventional handrails have certain key or essential components.
In this specification, including the claims, the structure of a handrail is described, as oriented on the upper run of a handrail balustrade, in a normal operational position. It will be appreciated that a handrail is formed as a continuous loop. Of necessity, any part of the handrail will travel around the entire loop, and during passage around the loop will rotate through 360.degree. about a transverse axis. The structure of both the handrail of the present invention, and conventional structures are all described relative to a vertical section taken through a top, horizontally extending run of the handrail.
A conventional handrail has a main, top portion, forming a main body of the handrail. Extending down from this top portion are two C-shaped or semi-circular lips. The main body and the lips define a T-shaped slot which opens downwardly and which has a width much greater than its height. The thickness of the handrail through the main body and the lips is usually fairly uniform.
As to the main or common components of a handrail, the body and lips are usually formed from a thermoset material. Some form of stretch inhibitor is provided along a neutral axis in the top portion, generally spaced just above the T-shaped slot. This stretch inhibitor is commonly steel tape, steel wire, glass strands or Kevlar cords.
To ensure that the handrail glides easily along guides, a lining is provided, around the outside of the T-shaped slot. This lining is sometimes referred to as a slider, and commonly is a synthetic or natural fiber based textile based fabric. It is selected to provide a low coefficient of friction relative to steel or other guides. The outside of the main body and the lips are covered with a cover stock, which is a suitable thermoset material.
Within the basic handrail profile, there can be selected plies, as detailed below, to provide desired characteristics to the handrail.
Now, a handrail has to meet a number of different requirements, many of which can conflict with each other. In conventional handrails, these are often addressed by introducing a number of different elements, in addition to or as variations of those outlined above. This is quite feasible in a conventional handrail structure, which is formed from a thermoset material. Conventionally, handrails are made stepwise or incrementally in lengths of approximately 3 m at a time, corresponding to the length of the vulcanising press. Thus, all the various elements required for a handrail, e.g. layers of fabric, layers of fresh, uncured thermoset material, tensile reinforcing elements are brought together. If fabric plies are incorporated, these are provided coated in uncured rubber. Thus, all the layers present uncured, tacky rubber surfaces, and these are pressed together either manually with rollers or by assembly equipment. The necessary length of these assembled elements is placed into a mold. There, the necessary temperature and pressure are applied, to vulcanize the thermoset material, and ensure that the elements together adopt the desired profile defined by the mold cavity. Once cured, the mold is opened, and the cured section moved out of the mold, to bring in the next length of already assembled elements for molding.
This technique has a number of disadvantages. It is slow, it produces the handrail in only incremental lengths, and it can result in a poor finish with mold markings. It does, however, have the advantage that relatively complex structures can be assembled, with numerous different elements, designed to give different characteristics.
The inventors of the present invention have developed a technique for extruding handrails from a thermoplastic material. This has the great advantage that the handrail can be produced essentially continuously and at a greater speed. The handrail can have a consistently high and uniform external appearance, which is highly desirable in a product that is one of the most visible elements of an escalator or handrail installation and which is gripped by users.
However, extruding the relatively complex structure of a handrail is not simple. Others have made proposals for extruding handrails, but to the inventors' knowledge none of these have been successful; this is believed to be because of the difficulty in reliably and consistently bringing the various elements together. In particular, techniques from the known art of batch or piecewise molding of handrails from thermoset material cannot simply be incorporated into an extruded handrail. Rather, techniques from such batchwise molding are inapplicable to a continuous, extruded molding technique.
More particularly, older techniques which simply teach introducing additional layers to give desired strength and other characteristics are simply inapplicable to an extruded handrail. For conventional molding operations where the various layers are pre-assembled, it is usually a relatively simple matter to introduce one or more additional layers. This may require a certain element of care and skill in assembling the handrail and it may increase the cost, but it is possible and it does not fundamentally alter the various steps in the molding operation.
In contrast, considered as a thermoplastic extrusion operation, extrusion of a basic handrail structure is already a complex operation involving a number of separate elements, with care having to be taken to ensure that they each are in the correct location in the finished profile; for example, the tensile elements must remain in the correct plane, while the slider fabric must be shaped to the relatively complex profile of the slot of the handrail. To introduce additional layers or plies is thus extremely difficult, and costly as it requires extra plies to be prepared by slitting and possibly coating with adhesive.
Considering now the characteristics that a handrail must meet, these essentially relate to its ability to remain on handrail guides and to be driven. Thus, the lips of the handrail must have sufficient strength to prevent derailment or detachment from the handrail guides. This is usually determined by measuring the load or force for a given lateral deflection of the lips. The spacing between the lips of the lip dimension must also be correct and be constant or maintained, within specific tolerances, throughout the handrail life. To introduce additional strengthening layers or plies is extremely difficult.
As to drive characteristics, there must be adequate friction between the handrail and a drive unit and the handrail must not be damaged by loads applied by a drive unit. One technique is to pass the handrail around a relatively large diameter pulley which engages the inner surface of the handrail, and often causes the handrail to be bent backwards to increase the contact with a drive wheel. While this could give adequate drive characteristics, it had a number of disadvantages. Such a drive requires a relatively large space, and passing the handrail through a reverse bend can cause undesirable stresses resulting in shortening of the handrail life.
Another technique is the use of so-called linear drives, which are the preferred system in some parts of the world. In a linear drive, the handrail is simply passed through one or more pairs of rollers, which are pressed against the handrail. For each pair of rollers, one of the rollers simply acts as a follower wheel or pulley, while the other is driven and acts to drive the handrail. To ensure adequate transmission of the drive force, the pairs of pulleys or wheels are pressed together with very high forces. This can impose very high internal stresses on the handrail causing a number of problems. The shear stresses generated in the nip between the pair of wheels can cause delamination of the plies in a conventional rubber, thermoset product. For tensile elements formed from stranded, twisted steel wire, glass yarns and the like, the stresses can cause a grinding action, resulting in fretting fatigue.
However, linear drive characteristics are desirable for a number of reasons. They eliminate the reverse bend problem of other drive units. They are more compact, and hence desirable, for example in escalator installations which have a transparent balustrade, limiting the space available for the handrail drive and reducing the length of handrail required. Also, for different sized installations, it is simply a matter of increasing the number of drive rollers to match the size of the installation.
A number of techniques have been proposed in the art for providing a conventionally molded handrail with the desired characteristics. However, many of these are relatively complex, and are only generally applicable to conventional piecewise molding techniques for thermoset materials. Thus, U.S. Pat. No. 5,255,772 is directed to a handrail for escalators and moving walkways with improved dimensional stability. This is essentially achieved by providing a sandwich structure in which two layers of plies are provided on either side of a layer of rubber composition in which the steel wires or other tensile members are embedded. This is preferably a higher strength rubber, so that a structural sandwich composition is formed with the two layers of plies.
Importantly, the two opposing layers of plies in this structure have their stiff principal yarns extending perpendicularly to the stretch inhibitor and hence perpendicular to the steel cables of the stretch inhibitor. The intention here is to improve the bending strength of the lips in response to lateral forces tending to deform the lips outwards.
However, such a structure is complex and has numerous different layers. It would be exceedingly difficult to form such a structure by extrusion. In addition to the basic elements listed above, it would, somehow, require the introduction of two additional plies of fabric material, which would have to be located at exact configurations within the extruded handrail.
Alternative approaches, allegedly suitable for extruded handrails, are found in U.S. Pat. Nos. 3,633,725 and 4,776,446. In the first of these patents, there is proposed a somewhat unusual structure in which an internal portion of the handrail is provided with a toothed structure to facilitate driving and also to facilitate bending. Then, a separate cover is provided. U.S. Pat. No. 4,776,446 provides so-called wear strips on the insides of each of the lips. These are intended to provide two functions, namely to provide a low co-efficient of sliding and improve the lip strength. These are constructed from a stiff, plastic material, e.g. nylon. It is suggested that they be co-extruded with the handrail, although no extrusion technique is disclosed. To permit these wear strips to flex, they are continuous on one side and provided with slots separating the other side into a row of leg portions. However, this simply forms stress concentrations and these relatively ridged wear strips would suffer cracking and flex fatigue, in use, due to repeated bending.